Impacts of human activities on the evolution of estuarine wetland in the Yangtze Delta from 2000 to 2010

The wetland in the Yangtze Delta plays an important role in coastal protection against erosion, water purification, and habitat maintenance of migratory birds. The Yangtze Delta is one of the largest economic zones (e.g., Shanghai) in China. Human activities severely affect wetland evolution. Wetland mapping was performed from multi-temporal remote sensing data of Landsat during the period 2000-2010 at intervals of about 5 years, and spatiotemporal changes in wetland characteristics as well as driving forces for such changes were analyzed. Results indicated the Yangtze River estuarine wetland area experienced a net increase of 63 % during the period of 2000-2010; from 2005 onwards, however, the rate of increase has decreased. Human activities, including upstream dam construction, estuarine engineering, land reclamation, and ecological engineering, played an important role in wetland evolution during this short period. Reduction of riverine sediment loads led to decreases in the increase rate of estuary wetland; 95 % of the estuarine shoreline is embanked by seawalls, which exerts negative effects because closure promotes substantial degradation of wetland areas. Urbanization and expansion of Shanghai facilitated regular land reclamation of wetland and led to 35 % wetland loss. Intentional artificial planting of aquatic plants and groyne construction accelerated sediment deposition and wetland formation to compensate for coastal wetland loss.